Eris provides a generic 'Entity' class, which you are free to sub-class and provide to the system (by registering a factory with the World); thus you are free to create different classes to handle characters, walls, vehicles, etc as your client dictates. An alternative approach is to simply create peer classes, and connect them to Eris via callbacks. Eris makes extensive use of libSigC++, which must be correctly installed and functioning on your system. Familiarity with signal/slot programming concepts is essential for using Eris; the libSigC++ home-page has some examples. Gtk+ or QT signal systems also provide a good introduction.